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Definitely agree with the rock work but I must stress the important with the sexing. Chances are that the lab that is the aggressor is a male. And chances are the ones he's chasing are male as well. I currently have labs among others and at one point had a troublesome male. The problem with this one was that he would try to spawn with my female and they wouldn't give him the light of day. I had 1m/4f ratio. When they wouldn't spawn he would rage it seemed and would chase to the point that the females would be winded and cowering at the top corner of the tank. I rehomed him and bought a juvenile male. All is well now and have 2 females holding. In the very beginning of it all I had 3 males and the sole survivor was the worst. The best thing I believe you could do is start over. If the money isn't an issue I would rehome what you have and order what you want thru Davesfish.com. A little pricey cause of the shipping but is well worth it. Not a single complaint about mine.

Now with the rock work. There must be enough hiding spots for every fish to hide. In a 125 I would have 3 large rock piles, one in the middle and one in each end. Out of sight, out of mind comes into play.

What are the parameters of your water. Malawis need hi ph 7.8-8.4. Harder water and warm temps. With the temp of the water, the warmer the more aggressive usually. I like to keep mine at 78 on my mbuna and tang tank. One other thing with the water is how often are you doing water changes? In a 125 you should be doing say a 30% water change weekly for having only 18 in such a large tank. The percentage can go up and how many time you do the change can go up as well. Depends on how much food is being wasted. Spot cleaning any visual waste a few times a week. Because of this, sand is highly recommended as for the waste settles on the surface and doesn't fall and get trapped in the gravel. Makes for easier cleaning. I normally use a 6 foot 3/4" silicone tubing from any hardware store.

How often are you feeding them? Too seldom and you get aggression, too frequent and you get fat cichlids. Africans play he puppy dog look very well. Have to find that happy medium.

Africans from Malawi are very high maintanance and you have to have the time and patience with them. If you don't everything can go to hell. Rethink and make sure that mbunas are for sure what you want to do and do a little research on the web. You'd be surprised on what you find.

I had this problem with a Red Zebra in one of my mbuna tanks. I also had this issue with a cobalt zebra at another time. Turns out that the reason why they both were aggressive because there was spawning in the tank and they were getting protective. After the female had her babies, the aggressiveness went away. I've also changed around the layout of the rocks before to fix this issue.

All in all, I've had 3 55 Gallon mbuna tanks in the past few years and this problem is very rare for me.

Keep in mind that I've never vented them. I have no clue what the M:F ratio is, nor do I care.

I also really don't care when people say do not keep Kenyi's with Red zebras and yellow labs. I've been keeping Kenyi's for 3 years now and they are among the most peaceful africans I have.

Another important fact about my tanks is that I overstock them. I have:

22 in a 55G
17 in a 55G
23 in a 55G

People act like they know everything and what they have experienced is the only way to keep africans. I see a lot of people high in their horse in these forums and other african forums thinking they know it all. The fact is, there are many different layouts, combinations, sizes, landscapes, water params, water temp, feeding schedules, breeding habits, etc....

I've had issues with all 3 of my tanks. Generally after 4-6 months of the tank being established, the problems all go away. I've gotten very lucky though. To this day, all of my tanks are in perfect order.

I believe overstocking african cichlid tanks are IMPORTANT. Overstocking african cichlid tanks spread out the aggression, calm the fish down. It doesn't allow 1 cichlid to claim an area. I've had major prorblems when I only had 12 africans in a 55G. Those problems disappeared with all 3 of my african tanks when I got 20+ africans in there.

All three of my tanks have 50-70 lbs of rock in them each stacked up with lots of hiding places. I have about 12-15 rocks in each tank. One has blue/black gravel. One has black gravel. One of them has black sand.

I have never had plants in my african tanks. Only rocks and substrate.

If you decide to overstock like many african cichlid owners have, I suggest 10x filtration. On my 55 gallon tanks, I have 685 GPH of filtration. I do 25% water changes once per week and my params are never higher than 0, 0, 40. They stay close to 0, 0, 10.

I might get flamed from know-it-alls, but there are a lot of people that believe in overstocking africans for taking away aggression. Just make sure that everyone is fed and there is a lot of hiding places.

That is Very easy to say BUT Do you know how hard it is to sex some of these fish?

I always LMAO when people tell me to sex all of the fish. Many fish you have to wait until they are adults to sex them. I've never even attempted to pick up each of my 45 fish and sit there sexing them. Not only would that take weeks to do, but it's impossible sometimes with juvies. I'm kinda giggling over here just thinking about me holding each slimy delicate fish in the air above my head looking for a stupid vent dot. Heck, i'd probably get it wrong and it wouldn't even matter anyways.

I think that telling him he shouldn't have even kept the fish in the first place is hardly the way to solve the issue... anyways...

I know that, but he could've solved the issue when he purchased the bigger tank and the other fish. I am just unsure what was on the OP's mind that time.

Anyways, i think the best possible solution is to take out the fish that is bullying everything. It's not easy, i know, but it's also harder to see all your fish get stressed out because of a single fish (or so).

I had this problem with a Red Zebra in one of my mbuna tanks. I also had this issue with a cobalt zebra at another time. Turns out that the reason why they both were aggressive because there was spawning in the tank and they were getting protective. After the female had her babies, the aggressiveness went away. I've also changed around the layout of the rocks before to fix this issue.

All in all, I've had 3 55 Gallon mbuna tanks in the past few years and this problem is very rare for me.

Keep in mind that I've never vented them. I have no clue what the M:F ratio is, nor do I care.

I also really don't care when people say do not keep Kenyi's with Red zebras and yellow labs. I've been keeping Kenyi's for 3 years now and they are among the most peaceful africans I have.

Another important fact about my tanks is that I overstock them. I have:

22 in a 55G
17 in a 55G
23 in a 55G

People act like they know everything and what they have experienced is the only way to keep africans. I see a lot of people high in their horse in these forums and other african forums thinking they know it all. The fact is, there are many different layouts, combinations, sizes, landscapes, water params, water temp, feeding schedules, breeding habits, etc....

I've had issues with all 3 of my tanks. Generally after 4-6 months of the tank being established, the problems all go away. I've gotten very lucky though. To this day, all of my tanks are in perfect order.

I believe overstocking african cichlid tanks are IMPORTANT. Overstocking african cichlid tanks spread out the aggression, calm the fish down. It doesn't allow 1 cichlid to claim an area. I've had major prorblems when I only had 12 africans in a 55G. Those problems disappeared with all 3 of my african tanks when I got 20+ africans in there.

All three of my tanks have 50-70 lbs of rock in them each stacked up with lots of hiding places. I have about 12-15 rocks in each tank. One has blue/black gravel. One has black gravel. One of them has black sand.

I have never had plants in my african tanks. Only rocks and substrate.

If you decide to overstock like many african cichlid owners have, I suggest 10x filtration. On my 55 gallon tanks, I have 685 GPH of filtration. I do 25% water changes once per week and my params are never higher than 0, 0, 40. They stay close to 0, 0, 10.

I might get flamed from know-it-alls, but there are a lot of people that believe in overstocking africans for taking away aggression. Just make sure that everyone is fed and there is a lot of hiding places.

Good luck.

I believe this is exactly why you have to be dedicated to observing and adjusting your tank as conditions change especially when keeping Africans, not just Malawi. No two tanks are the same. You can have the same species of fish in two different tanks, with one being a peaceful community and the other being a war zone. It's a classic "what works for me may not work for you" scenario. IMO, in the vast majority of rift lake tanks, there will inevitably be some sort of an issue, small or big. It's the nature of the beast. Research and planning can alleviate a lot of the potential. Being prepared, having the ability to spot a developing problem, and how you handle and remedy the situation, all play a hand in being successful with them.

....Still my alpha targeted one lab and actually killed it. Then he started bullying another yellow lab so I took the alpha out. Within an hour the bullied fish became really mean and pushed all the other fish to one half of the tank. I was upset and put the alpha back to restore some peace even though that means having the bullied one cowered in the corner all the time....

I've actually had this happen before as well. The alpha male of a particular species constantly harassed the four other members of his own kind and kept the sub-dominant male holed up in a cave; but left all of the other mbuna species alone. I removed this alpha male and within hours the sub-dominant male became a terror in the tank, harassing his own species and every other fish in the tank and tried to lay claim to 1/3rd of a 125gal tank. I returned the original male and order was restored immediately (the tyrant returned to his hole).

Removing the sub-dominant male yellow lab may solve the problem since it appears that alpha male only has a problem with other male yellow labs.

It's interesting how these fish sense and take advantage of 'power vacuums'.

From what I've seen in my mbuna tanks the most hazardous scenario that can occur is when a dominant fish is able to achieve exclusive one-way aggression and combine that with the ability to single-out its 'target'. Hiding spots may be rendered ineffective at this point because the aggressor is usually in perpetual hunt and destroy mode at this time.

Increasing the overall tank population, as SW Florida Kid suggested, does make it harder for the aggressor to lock on to a particular fish (depending on variables, of course).

Ovestocking may need to be tailored toward the specific aggression problem, though. In some cases one may need increase the number of a particular species or particular gender of a certain species.

Years ago my 75gal contained over 24 demasoni's, 6 (2m/4f) msobo's, a trio of socolofi's and a BB zebra, equating to over 34+ fish in the tank.

However an overly-aggressive female msobo was still able to kill two other female msobo's and nearly fished off the last female in a single afternoon. The overall mbuna numbers in the tank counted for nothing and weren't enough to deter or impede her because demasoni's, BB zebra's and socolofis or male msobo's weren't on her 'hit list'.

As far as she was concerned the other 3 females in the tank had to go and it was easy for her to pick them off in a single day (and this happened following a number of years of co-existence with little female vs female aggression up until that point).

I now keep msobo's in a smaller tank (55gal) with the female msobos being somewhat overstocked: 10+ females more so to diffuse female vs female aggression than placate the males.

Nearly all of the mbunas in my 125gal were born in the tank and their gender ratio's have not been controlled by me. I think I have an over-abundance of male yellow labs. They scrap and challenge each other all the time, more so than the "aggressive species" in the tank. However not one of these labs has been able to attain 'alpha male' status which means their encounters are never one-sided and there are multiple contenders, the outcome of their rivalries mostly being 'draws'.

Even when the tank is fairly peaceful, it still has to be monitored for aggression because these fish can sense and take advantage of signs of weakness in the pecking order of the tank. I've had sub-dominant males which, following years of being submissive to the dominant male, decide one day that they can overthrow and nearly kill the alpha male.

I've had a African cichlid tank for 2 years. There's only 3 fish in it now. If a fish was overly aggressive I'd give it to my local aquarium store. The result is that I have 3 of the most laid back easy going Mbuna's you could imagine. 2 acei's and 1 yellow lab. Now I know you might not want just a few fish and that's understandable but I just thought I would share my story because I'm more happy with my Mbuna tank in the past 6 months then I ever have been before since it's just the 3 of them. They are beautiful and thriving. My acei's are huge!

This peaceful tank of mine may be just a lucky fluke. I realize that experienced African cichlid keepers most likely will not agree with my method for this tank, it's simply just an unusual method that was successful for me. Best of luck with your tank.

I've had a African cichlid tank for 2 years. There's only 3 fish in it now. If a fish was overly aggressive I'd give it to my local aquarium store. The result is that I have 3 of the most laid back easy going Mbuna's you could imagine. 2 acei's and 1 yellow lab. Now I know you might not want just a few fish and that's understandable but I just thought I would share my story because I'm more happy with my Mbuna tank in the past 6 months then I ever have been before since it's just the 3 of them. They are beautiful and thriving. My acei's are huge!

This peaceful tank of mine may be just a lucky fluke. I realize that experienced African cichlid keepers most likely will not agree with my method for this tank, it's simply just an unusual method that was successful for me. Best of luck with your tank.

Slightly off topic but all male mbuna tanks are possible with 3-6 specimen depending on tank size, and they look beautiful.

I've got a 110 gallon mbuna tank and I dont even know how many fish are in it... probably 60? Mix of males and females and I do have a lot of rock in there. No excessive aggression towards any one fish its pretty evenly distributed between them all lol. My experience with these fish is the more there is the less aggression there is. The problem I'm having is that they keep breeding! I get 10+ surviving fry almost every month. So I guess that may be a downside to over populating.